The present invention relates to polyurethanes combined with or applied to another material and a process for their production.
The manufacture of polyurethanes, optionally in cellular form, which have been prepared or combined with another material is known. For example, PVC foils are back-foamed with a polyurethane and the composite so obtained is used on a large scale for example for automotive seats, covered neckrests or dashboards.
Due to reduced air drag in automobiles and strongly curving windshields and rear windows, the inside automobile temperature rises substantially upon exposure to sunlight. Consequently, the requirements for an acceptable composite made of PVC foil and polyurethane foam have increased. For example, composite dashboards subjected to higher thermal stress become brittle and may break up and the PVC cover layer progressively discolors. Damage to the polyurethane (PUR) foam is also observed. Strong degradation of the cover foils also occurs.
U.S. Pat. No. 3,281,379 discloses the addition of epoxides in order to prevent the self-discoloration of polyurethane foams following heat aging. The present invention, however, is directed to suppression of the damage to a cover layer combined with a polyurethane foam from thermal effects. It has now been found that adding epoxides to an expandable reaction mixture--while not preventing foam discoloration upon prolonged thermal exposure--renders the cover layer color-stable and that this cover layer remains unchanged in its polymer properties and structure.
German Offenlegungsschrift 2,933,173 discloses a costly composite of a thermally cross-linking bonding layer between the foam and the cover layer in which copolymers containing carboxyl groups and deposited on a cover layer are thermally cross-linked and then are back-foamed with an expandable polyurethane reaction mixture. This publication does not however mention the problem addressed by the present invention nor suggest its solution.